1 files changed, 88 insertions, 0 deletions
diff --git a/2018/src/day5.rs b/2018/src/day5.rs
new file mode 100644
index 0000000..4638858
--- /dev/null
+++ b/2018/src/day5.rs
@@ -0,0 +1,88 @@
+use std::io;
+use std::io::BufRead;
+
+fn reactive(a: u8, b: u8) -> bool {
+    a == b + 32 || b == a + 32
+}
+
+fn react(line: &mut [u8]) -> usize {
+    let len = line.len() as i64;
+    let mut gone = vec![false; len as usize];
+
+    let mut top: i64 = 0;
+    for ptr in 1..len {
+        if top >= ptr {
+            continue;
+        } else if reactive(line[top as usize], line[ptr as usize]) {
+            gone[top as usize] = true;
+            gone[ptr as usize] = true;
+            top -= 1;
+            while top > 0 && gone[top as usize] {
+                top -= 1;
+            }
+            if top < 0 {
+                top = ptr + 1;
+            }
+        } else {
+            top = ptr;
+        }
+    }
+
+    let mut j = 0;
+    for i in 0..len as usize {
+        if !gone[i] {
+            if j < i { line[j] = line[i]; }
+            j += 1;
+        }
+    }
+
+    j
+}
+
+fn full_react(bytes: &mut Vec<u8>, mut len: usize) -> usize {
+    loop {
+        let newlen = react(&mut bytes[..len]);
+        if newlen == len { break; }
+        len = newlen;
+    }
+
+    len
+}
+
+// Pass 'typ' as uppercase.
+fn remove_type(dest: &mut [u8], src: &[u8], typ: u8) -> usize {
+    let mut j = 0;
+    for i in 0..src.len() {
+        if src[i] != typ && src[i] != typ + 32 {
+            dest[j] = src[i];
+            j += 1;
+        }
+    }
+
+    j
+}
+
+pub fn main<T: BufRead>(reader: T) -> io::Result<(String, String)> {
+    let line = reader.lines().next().unwrap().unwrap();
+    let mut bytes: Vec<u8> = line.bytes().collect();
+    let mut len = bytes.len();
+
+    len = full_react(&mut bytes, len);
+
+    let part1 = len;
+
+    let mut minlen = len;
+
+    let mut bytes2 = bytes[..len].to_vec();
+    for typ in 65..65+26 {
+        let newlen = remove_type(&mut bytes2, &bytes[..len], typ);
+        let len2 = full_react(&mut bytes2, newlen);
+        if len2 < minlen {
+            minlen = len2;
+        }
+    }
+
+    let part2 = minlen;
+
+    Ok((part1.to_string(), part2.to_string()))
+}